The invention relates to a mill classifier, particularly a roller mill classifier according to the preamble of claim 1.
Roller mill classifiers, which can be arranged in integrated manner in or mounted on a roller and bowl mill or in a roller mill, e.g. in an air-swept mill, can be constructed as static or dynamic sifters or classifiers. Combinations of a static and a dynamic classifier, which is then referred to as a high effect classifier, are also known.
A high effect classifier is described in ZKG, vol. 46, 1993, No. 8, pp 444 to 550, FIG. 7. The classifier has a cylindrical strip rotor and a concentrically arranged guide flap or vane ring. The aim is to produce a very effective tangential flow between the static distributor and the strip rotor, so that the coarse particles cannot reach the rotor. The disadvantages are an increased pressure loss and an increasing wear to the guide vanes, particularly with high particle concentrations.
EP 204 412 B1 discloses a mill classifier, which has two superimposed guide vane rings. The guide vanes are adjustably arranged about vertical spindles, the guide vanes of the guide vane rings having independently mounted spindles. Between the guide vane rings is provided a stationary ring and the adjusting devices are located at opposite ends of the guide vanes.
FR 2 642 994 A1 discloses a classifier with a strip rotor and a concentrically arranged guide vane ring. In order to improve classification the guide vanes of the guide vane ring are adjustable about a vertical axis. The rotor strips are constructed in such a way that in each case channels are formed with a cross-section widening from the outside to the inside, so that the centrifugal and resistance forces acting on the particles of a predeterminable size, are in equilibrium over virtually the entire length of the channels. Thus, the equilibrium conditions are obtained via the profile of the rotor strips, the rotor speed and the setting of the guide vanes for different separating diameters.
The cylindrical strip or rod basket rotor used in the afore-mentioned mill classifiers generally has a number of strips, which is at least twice as high as in so-called standard classifiers, which leads to relatively high manufacturing costs. The suspension and mounting of a rod basket rotor also differs from the rotors of the standard classifier and contributes to higher manufacturing and assembly costs.
A known standard classifier is the LOESCHE centrifugal/basket classifier of the LKS design (ZKG, vol. 46, 1993, No. 8, p 446, FIG. 5). This dynamic classifier is constructed as a biconical or double cone strip rotor and has a double cone rotor with screwed on classifying strips. The sloping rotor strips correspond to the incident flow from below and lead to a weak deflection of the grinding material-fluid flow. In conjunction with a twisting flow caused by the setting of the blades of a blade ring of the mill and a conically upwardly widening classifier casing, a radial flow occurs at the strip rotor and increases from bottom to top and leading on the conically upwardly widening strip rotor to different centrifugal forces and to a relatively uniform classifying over the entire strip length.
DE 44 23 815 C2 discloses a high effect classifier, in which a static classifying precedes a double cone rotor of a LOESCHE centrifugal/basket classifier. By means of at least two axially superimposed and adjustably arranged guide vane rings and a directional deflection of the grinding material-fluid flow, part of the coarse material is separated, before a dynamic reclassifying takes place through the following conical strip rotor. The classifier has an improved separation efficiency and a lower energy consumption compared with standard classifiers, but does not in all cases meet the constantly increasing demands on efficiency and low manufacturing and maintenance costs.
The object of the invention is to provide a mill classifier, particularly a roller mill classifier, which in the case of particularly simple construction has very low production costs and simultaneously permits a high flexibility and optimization of sifting or classifying processes.
According to the invention the object is achieved by the features of claim 1. Appropriate and advantageous developments appear in the specific description relative to the drawings and in the sub claims.
A fundamental idea of the invention is to retain the advantages of a strip rotor of a LOESCHE centrifugal/basket classifier and to achieve a purely dynamic classifying with the aid of at least one guide vane ring, the guide vanes and the rotor strips being so constructed and mutually oriented that the grinding material particles are not forced onto an orbit outside the strip rotor and are instead delivered into the strip rotor.
According to the invention the guide vanes are shaped and positioned in such a way that there is no so-called cyclone flow, but instead and without an upstream static classifying stage, a grinding material-fluid mixture is directly dynamically classified.
According to the invention a roller mill classifier with a strip rotor of a fundamentally known design and a guide vane ring arranged concentrically around the strip rotor is provided with flow-optimized guide vanes, which are adjustable about a vertical rotation axis and force a grinding material-fluid flow rising from the mill to a tangential to radial incident flow of the rotor strips of the strip rotor.
Preferably use is made of rotor strips, as are known in connection with LKS classifiers, but at least in the vicinity of the guide vanes are arranged vertically and therefore parallel to the guide vanes.
It is appropriate with respect to the production costs and efficient classifying to use as the strip rotor a double cone rotor, particularly of a LKS design LOESCHE centrifugal/basket classifier and to retool or reset the same in such a way that the known rotor strips are retained, but are perpendicular and no longer slope to a cylindrical rotor area. As the rotor strips have a radial dimensioning as with a LKS classifier, it is possible to significantly reduce the number of rotor strips compared with the cylindrical rod basket rotors of the high effect classifier. It has been found that the number of strips can be approximately one third of that of a rod basket classifier and can be max 50%.
A separation-efficient classifying without an upstream static classifying can be achieved by at least one guide vane ring with flow optimized guide vanes, which have a rounded leading edge and at least one guide plate and which are set with respect to the strip rotor in such a way that an imaginary extension of the guide plates does not extend past the strip rotor and instead leads at least tangentially to the outer edges of the rotor strips or radially into the rotor centre.
It is particularly advantageous to have guide vanes with a rounded leading edge and at least one guide plate located thereon in such a way that roughly parallel or widening flow channels are formed between in each case two guide vanes and the incoming and outgoing flows are approximately the same.
In conjuncation with the rounded leading edge there is a parallel flow without constriction during the outgoing flow and as a result of a particularly advantageous streamlined construction of the guide vanes there is an expanding outgoing flow with a diffuser effect, which is linked with a recovery of pressure energy and therefore a reduction of the through-flow resistance of the classifier. However, in the case of planar guide vanes a flow channel with a nozzle effect is formed between two guide vanes.
A cost-effective manufacture, assembly and simple adjustment of the flow-optimized guide vanes can be achieved in that the rounded leading edge is constituted by a cylindrical or tubular incident flow body, e.g. an incident flow tube, on which the guide plate is arranged, e.g. welded tangentially. It is also possible to indirectly fasten the guide plate, e.g. by means of an additional fastening plate to the incident flow tube. Whereas the fastening plate, which can be kept relatively narrow, can be fixed directly to the incident flow tube, the guide plate can be detachably fixed, e.g. screwed to the fastening plate. Thus, if the guide plate wears, a relatively rapid, inexpensive replacement is possible.
Appropriately the incident flow tube is circular cylindrical and made from an abrasion-resistant material, the rotation axis of the guide vanes being formed by the longitudinal axis of the incident flow tube. This leads to the advantage that both the mounting support for the guide vanes, e.g. by means of swivel pins, in the vicinity of the classifier housing, and the adjustment from outside the classifier housing can be performed in an extremely favourable manner.
Streamlined guide vanes are particularly advantageous for flow channels with a diffuser effect and can e.g. be formed by two guide plates, which are tangentially fixed to the incident flow body or tube. It is advantageous for manufacture and mounting if both guide plates have a substantially identical construction and engage on one another with rotor-side edge regions, i.e. taper off. However, the second plate can also be narrower than the guide plate facing the classifying material flow and can be fixed with a different setting angle to the guide plate facing the classifying material flow to the incident flow body, in order to bring about an opening flow channel with diffuser effect.
It has been found that a separation-efficient classifying can be achieved with a strip rotor and at least one guide vane ring having an identical number of rotor strips or guide vanes. In principle, the rotor strips can have a Z-shaped construction.
An advantageous, flow-optimized form of the Z-shaped rotor strips can be achieved if the legs directed towards the guide vanes are rounded. As a result of this rounded Z-shape there is a reduced resistance compared with the conventional angular shape. In addition, the flexural stiffness of the rotor strips is increased, which is particularly advantageous with an overhung arrangement.
In order to achieve a direct dynamic classifying over substantially the entire rotor area, the heights of the guide vanes and the rotor strips are matched to one another. In the case of a strip rotor, which corresponds to a retooled double cone rotor of a LOESCHE centrifugal/basket classifier, the cylindrical rotor area above a conical rotor area is to be dimensioned in such a way that the vertical rotor strips of the cylindrical rotor area have roughly the same height as the concentrically arranged guide vanes of the guide vane ring. The conical rotor area can be made hydraulically ineffective advantageously by means of a cover, e.g. a cover cone, which is located between the cylindrical and the conical rotor area. As the strip rotor with its conical rotor area already functions within the oversize material return cone, there is no need to cover in a jacket-like manner said area or the conical strip ends.
Appropriately for the mill classifier according to the invention not only are the rotor strips of the strip rotor constructed as for a LKS, but also the classifier housing, or at least its upper part, the bearing collet, as well as the drive and driving shaft can be constructed as in a LOESCHE centrifugal/basket classifier. It is advantageous to omit the lower cone of the double cone rotor and to have a shortened construction of the driving shaft. The classifier housing known from the LKS classifier can be fundamentally adopted, but the space for the rising grinding material fluid flow is constricted over the height of the guide vane ring, so that the particle flow is accelerated into the flow channels of the guide vane ring.
The mill classifier according to the invention makes it possible to supply the entire grinding material particles ranging from fine to coarse material, to the strip rotor for a purely dynamic classifying. After passing through the grinding gap between the grinding rolls and the grinding path, the particle flow is centrifuged into the fluid flow, flows upwards as a grinding material-fluid flow along the periphery of the grinding bowl and is transported through the guide vane ring, without prior separation of coarse particles, into the strip rotor. The strip rotor by centrifugal separation separates the coarse particles from the overall particle flow, in that the coarse particles are centrifuged by the strip rotor against the guide vane ends, where they drop by gravity as oversize particles into the coarse material return cone.
It falls within the scope of the invention to provide more than one guide vane ring over the height of the cylindrical rotor area of the strip rotor and to equip the guide vanes of each guide vane ring with an adjusting device. It is advantageous to position a thrust ring below the guide vane ring.
It also falls within the scope of the invention, to use in place of a retooled rotor of a LOESCHE centrifugal/basket classifier, a rod basket classifier of a high effect classifier and to provide same with concentrically arranged, flow-optimized guide vanes according to the present invention.
Essential advantages of the mill classifier according to the invention are relatively low manufacturing, assembly and installation costs due to the possible retooling of a LKS. In addition, through the possible retooling of a LKS, it is rapidly and inexpensively possible to comply with the wishes of customers for a separation-efficient, cost-effective mill classifier.